George Floyd died from a low level of oxygen that damaged his brain and caused his heart to stop, a medical expert testified Thursday in the trial of Derek Chauvin, the fired Minneapolis officer charged in Floyd’s death. Dr. Martin Tobin, an expert who specializes in pulmonology and critical care, was the first witness called to the stand on the ninth day of the trial.

Tobin, a Chicago-based physician who is a renowned expert in medical issues involving the lungs and respiratory system, testified that Floyd’s “shallow breaths weren’t able to carry air through his lungs, down to the essential areas of the lungs that get oxygen into the blood and get rid of carbon dioxide.”

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